Can hydrogen storage solve a renewable energy problem and drive net zero ambition?

There has never been a shortage of clean energy on Earth. The Sun alone bathes the planet in 200,000 times the world’s daily electric-generating capacity every day, and added to that there’s wind, tidal, geothermal energy and hydroelectric power – the list goes on. And the technology for harnessing these renewable energy sources is constantly improving. In 2019 the energy sourced from renewables in the UK had already reached 40% of the total supply, exceeding that from fossil fuels. That still leaves quite a way to go to reach net zero, though, which is why multinationals and governments are looking to hydrogen for help.

BP has announced more than 10 hydrogen projects across Europe, the USA and Australia, with the aim of producing 0.5-0.7 million tonnes of hydrogen per year by 2030. Likewise EDF has numerous large hydrogen projects underway, such as Tees Green, an electrolysis plant powered by local wind and solar farms, with a planned initial phase capacity of 7.5MW. Producing hydrogen that can later release energy as it oxidises – ‘burns’ – to form water provides stashes of ready energy when and where you want it – if you can store it.

“We were addicted to natural gas because it’s so turn off and onable,” says Tom Scott, Professor of Nuclear Materials and Spin-out Executive Director at the University of Bristol, talking to Bristol Innovations Foresight about the many ways in which hydrogen is the ideal replacement for gas. “You just can’t store it the same way. This is the conundrum.”

The storage challenge has not yet sparked the zeal in the industry’s big players that producing hydrogen has, and a dearth of government incentives may be partly to blame [See We need hydrogen energy storage to reach net zero, so it’s essential we start building it now]. However, there are researchers, start-ups and pockets of multinational companies progressing with solutions to navigate the complications of storing this highly volatile, reactive material in ways that are safe and economical, not just financially but also in terms of the energy and environmental costs.

Searching for hydrogen storage solutions

For a long time the most efficient way to produce hydrogen was steam methane reformation, termed ‘grey hydrogen’, which produces CO₂ . There has been enthusiasm from government and industry alike for carbon capture and storage schemes that promote grey hydrogen to the more environmentally friendly ‘blue’, but these are far from perfect.

A 2020 assessment of the sustainability of CO2 storage put the efficiency of carbon capture at just 6-56%, with the 30-50% fossil fuel required to capture released CO₂ further undermining the environmental benefits. Furthermore, producers of ‘green hydrogen’, using purely renewable energy sources, are starting to pip grey and blue hydrogen in terms of efficiency and cost. However, anything that relies on the likes of solar and wind energy is at the mercy of the British weather – clearly a means of storage is essential.

Hydrogen gas is incredibly light and volatile. A cubic metre would weigh just 80g. To find the kind of space needed to store hydrogen as a gas, a lot of people have looked underground to existing geological features. In 2021 Mitsubishi Power teamed up with Texas Brine to look into using underground salt caverns excavated with water to store hydrogen, and an underground salt cavern in Utah in the USA remains a key piece in the Advanced Clean Energy Solution Hub there. Salt rock structures are quite impermeable, so can trap not just green hydrogen but natural hydrogen formed through geological processes.

Care is needed though to establish the minimum and maximum gas pressure that will keep the structure stable. Natural underground hydrogen storage can also be prone to reactions with the minerals and microbes that form methane and other chemicals. This is less of an issue for hydrogen earmarked to blend with natural gas supplies, but poses a complication for fuel cells that require pure hydrogen. Thankfully, it probably isn’t a deal breaker. An encouraging recent assessment of the UK’s geological storage capability concluded that the UK’s peak domestic heat demands ‘can be met by hydrogen storage in salt caverns’. However space is not the only challenge when it comes to hydrogen storage.

Tim Blake, the largest shareholder of Hydrogen Future Industries (HFI) plc and the CEO of several of their US and UK subsidiaries, highlights the explosive hazard presented by compressed hydrogen gas. HFI has developed wind energy turbines that treble the energy harvesting efficiency of traditional blades, as well as fuel cell electrolysers capable of generating hydrogen with 97.1% efficiency. A lot of its work to decarbonise energy supplies focuses on the mining industry, which alone accounts for 10% of the world’s energy use.

“[The mining industry] has enough issues just getting things insured,” Blake tells Foresight. “If you have tonnes of compressed hydrogen on site, you will not get insurance because if there’s an issue, if something happens and that explodes, you’ve got a huge explosion.” 

Similar caution would seem appropriate when working in any well-populated region.

The storage challenge has not yet sparked the zeal in the industry’s big players that producing hydrogen has, and a dearth of government incentives may be partly to blame

Lower the temperature enough and you can liquify hydrogen to store at higher densities without the massive pressures used for compressed hydrogen gas storage. However, the boiling point of hydrogen is just -252.9°C so a significant amount of cooling is involved. According to the International Renewable Energy Agency “30-40% of the hydrogen energy content is used for the liquification [sic] process (compared to 15% in the case of compressed gas storage).”

In addition, the valves and tanks used become vulnerable to hydrogen embrittlement. Nonetheless in January 2022 the HESC project, delivered by a consortium of energy and infrastructure companies, successfully shipped liquid hydrogen between Australia and Japan. The consortium included Kawasaki Heavy Industries, J-Power, Iwatani Corporation, Marubeni Corporation, Sumitomo Corporation, and AGL. While this proved that shipping liquid hydrogen is possible, there is still demand for technological improvements and economies of scale to help with the financial and energy costs.

Unstable alternatives

Another liquid form that looked like a possible storage solution for a while was ammonia. It has a high hydrogen content, and its manufacture is already a well advanced industry. However, the huge and tragic explosion of an ammonia factory in Beirut in August 2020 heightened safety concerns. Ammonia is not only highly explosive but also toxic, and plans for shipping have to bear in mind the risks when passing near areas with a high population density. For instance, ships passing through the Suez Canal have recently been prone to Houthi missile attacks.

“If you had an ammonia filled ship going through the Suez Canal and someone fired a missile at it that could be a catastrophic loss of life,” says Scott. “Shipping has said it’s not worth it.”

With all the problems associated with storing energy as hydrogen, you might well be wondering what’s wrong with just charging up a battery instead.

“We can take a multi-billion pound liability and turn it into a multi-billion pound asset”

Professor Tom Scott, University of Bristol

“It all comes down to what you want to use the power for,” says Blake, again citing mining, which is often based in remote locations such as Alaska where temperatures can sink below -30°C. Below freezing, a battery would not work well – but even if it did, you would need extensive expensive infrastructure to connect to the grid or you would have to charge from a diesel generator anyway.

“When you have huge dumper trucks of rubble,” Blake explains, “they would require 1-2MW of batteries – that can be up to 14-15 tonnes of lithium ion.” Charging such large batteries at a reasonable speed becomes a significant fire risk because of the waste heat generated, and these would barely last 40 minutes before they needed recharging.

While batteries can work well for smaller electric vehicles, when it comes to ‘grid smoothing’ to try and deal with supply and demand fluctuating out of sync, at Scott’s estimate a battery is only good for ‘a few minutes’.

“Even to power a medium sized village you’re talking about sports centre size battery packs,” he adds. “The amount of lithium you would need for that – there’s just not enough of it and the price goes up.”

Working with nuclear waste

Scott’s own research has centred around hydrogen storage for the past 20 years, but initially his target was fusion energy, which uses a 50:50 mixture of two hydrogen isotopes – deuterium and tritium – as the fuel. Scott and his colleagues found that by forming a hydride with depleted uranium – a nuclear fission energy waste material where the more radioactive isotope ²³⁵U has been mostly removed – they could store hydrogen at twice the density of liquid hydrogen. The UK government has hundreds of thousands of tonnes of depleted uranium stored in airtight ‘beds’. Simply passing hydrogen through these beds forms the hydride and some waste heat energy – add some heat and the hydrogen is released again.

Scott and his team are currently working with Hydrogen Future Industries to commercialise the technology, as part of a consortium including EDF UK R&D, the University of Bristol, the UK Atomic Energy Authority (UKAEA) and Urenco. The Business, Energy and Industry Strategy Net Zero Innovation Portfolio awarded the consortium £7.7m to develop the technology as HyDUS (hydrogen depleted uranium storage).

As well as preventing oxygen and water from getting in – as they would react vigorously – the HYDUS beds have a copper-based device inside that helps with efficient heat transfer in and out of the beds.

“Within a year we’ll hopefully have a structure that we can put forward to production,” says Blake.

According to Scott, the UK government already owns enough depleted uranium to meet half the country’s hydrogen storage demands.

“For the UK, we can take a multi-billion pound liability and turn it into a multi-billion pound asset,” he says.

It sounds compelling, and while other groups are looking at using other metal hydrides, such as alloys of magnesium and aluminium, which are much lighter than uranium, there is no definite, one-size-fits-all solution here. Scott’s own group is also looking at a lanthanum nickel alloy, which has a third of the weight by volume of uranium and releases hydrogen at just 25-30°C. It needs to be chilled to load the hydrogen, but for frozen goods delivery vehicles that could work well. However there would still be the need to source the lanthanum and nickel, which unlike depleted uranium is not already lying around the UK in hundreds of thousands of tonnes.

Prioritising hydrogen storage

Materials innovations are not the only way to improve prospects for metal hydride hydrogen storage. As H2GO co-founder and director Dr Enass Abo-Hamed explains, for its technology the specifics of the hydride material are irrelevant – the device works with a range of different materials with different hydrogen density hydrides.

“Where we claim credit is in building modular reactors around them,” she tells Foresight, highlighting the importance of heat management and optimisation, so that they can work with materials that have what she calls ‘dumb kinetics’ and make them excel. “That enables us to take something that is cheap, with a very well established supply chain that we can buy from manufacturers around the world, and make its performance superior with engineering instead of the material itself.”

As well as engineering structures to optimise heat management, the reactors at H2GO have a ‘digital brain’ that is capable of assessing when to generate hydrogen and when to store it based on pricing, as well as the supply and customer demand. The technology is now at a mature stage, has already been deployed and comes in modules that can adapt to the needs of different users.

However, in terms of companies working on the storage side of hydrogen energy technologies, Abo-Hamed feels she’s in a short queue.

“People think they need to wait to understand hydrogen storage until they have deployed hydrogen generation,” she tells Foresight. “That delay I think is unnecessary and could create hydrogen molecules that end up not being used when it makes most sense based on pricing and demand.”

It’s a familiar story. Speak to people working on large scale hydrogen projects planning to generate several MW of hydrogen power and ask them about storage, and the response can be a hazy plan to just ‘provide to offtakers’.

“They need to be looking into it more,” says Blake, who thinks a lot of people are “passing the buck.” He cites people touting ammonia as a solution because they are used to transporting ammonia. “It doesn’t mean it’s good. It doesn’t mean it’s safe. But it’s someone else’s problem.”

Abo-Hamed also flags how the scenario echoes the situation with solar cells, where batteries were deployed in a second wave once people finally recognised there was an intermittency problem.

“Storage is an issue and I think it needs to be developed hand in hand with generation,” she says. For all the difficulties facing hydrogen storage, she adds, “the challenge is getting industry to move at the right pace, where they adopt storage as fast as they adopt generation.”